Preparation,Modification And In Situ Raman Study Of Manganese-Based Electrode Materials

Manganese-based electrode materials are ideal materials for future large-sized rechargeable secondary battery due to their abundant raw materials,low price,environment friendly,good safety and other advantages.However,manganese-based materials still have drawbacks such as poor electrical conductivity,poor cycling stability and etc.,even some of them suffer from large volume changes and dissolution of Mn,making it difficult for large-scale commercial application.At present,most of the modification methods of manganese-based materials mainly focus on the combination with carbon-based materials and ion doping.In this thesis,two kinds of manganese-based electrode materials,ZnMn2O4 and P2-Na2/3Ni1/3Mn2/3O2,were prepared and modified,and good modification effects were obtained.Furthermore,in-situ Raman spectroscopy was employed to study the modification mechanism.(1)In view of the shortcomings of poor conductivity and poor cycle stability of ZnMn2O4 anode materials,we have modified it with Ag nanoparticles.Ag nanoparticles in Ag/ZnMn2O4 composite are uniformly distributed on the ZnMn2O4 substrate because they are prepared by coprecipitation method,which significantly improves the conductivity of ZnMn2O4.Electrochemical performance results show that the decoration of Ag could improve the first cycle coulombic efficiency,cycle stability and rate performance of ZnMn2O4.By comparing the surface morphology of the electrode materials before and after 30 cycles,we found that the addition of Ag may inhibit the continuous generation of SEI and improve the cycle stability of ZnMn2O4.(2)Layered manganese-based cathode material P2-Na2/3Ni1/3Mn2/3O2 usually undergoes P2-02 phase transition process in high-potential region during charge/discharge,which seriously affects the cyclic stability of this material.P2-Na2/3Ni1/3Mn1/3Ti1/3O2 obtained by Ti substitution shows better cycle stability than P2-Na2/3Ni1/3Mn2/3O2 under the same test conditions.It is found that after partial Mn was replaced by Ti,the transition metal layer in the unit cell is compressed,and the sodium layer is expanded,which reduces the diffusion energy barrier of sodium ions.Furthermore,the in-situ Raman method was employed to monitor the charge/discharge process of these two materials.The phase transition process of P2-Na2/3Ni1/3Mn2/3O2 occurred above 4.10 V,mainly concentrated at 4.15 V-4.25 V,while the phase transition process of P2-Na2/3Ni1/3Mn1/3Tii1/3O2 is between 3.80 V and 4.25 V,which is wider than P2-Na2/3Ni1/3Mn2/3O2,which leads to a slow phase transition process and the volume change is relatively moderate during the charge and discharge process.Ultimately,the material stability and cycle performance are improved.